Windows 10qcow2 -

Running Windows 10 on qcow2 can be nearly bare-metal fast with proper tuning.

Windows 10 tends to mark space as "free but not zeroed." To shrink the file after deleting files inside the guest: windows 10qcow2

Your QCOW2 file is fine, but UEFI/BIOS is wrong. Windows 10 needs UEFI + Secure Boot (or legacy BIOS). In virt-manager , go to Overview → Firmware: change to . Also add an OVMF (Open Virtual Machine Firmware) package. Running Windows 10 on qcow2 can be nearly